Tissue ablation is used in numerous medical procedures to treat a patient. Ablation can be performed to remove undesired tissue such as cancer cells. Ablation procedures may also involve the modification of the tissue without removal, such as to stop electrical propagation through the tissue in patients with an arrhythmia. The ablation is often performed by passing energy, such as electrical energy, through one or more electrodes causing the tissue in contact with the electrodes to heats up to an ablative temperature, but may also be performed by freezing the tissue with the use of a cryoablation catheter.
Cryoablation catheters typically include an expandable element, such as a balloon, at the distal end. Although there are significant advantages of using balloons for cryoablation techniques, there are often associated disadvantages. First, to provide adequate attachment strength between a balloon and the catheter, the distal end of the balloon is often attached to a device distal tip, which may extend distally beyond the balloon. A balloon catheter with a distal tip can be difficult to position within the body, for example the right or left atrium of the heart. For a cryoablation technique to be effective, the distal end must be articulated with great accuracy to contact the balloon with the target tissue. Additionally, this technique is often performed in a very small space. A catheter with a long distal tip (one that extends past the distal neck of the balloon) or a balloon with extended distal and/or proximal necks can contribute to this steering difficulty.
Second, there is the concern that the balloon will burst from the application of pressurized cryofluid within, or the seal between the balloon and the body or shaft of the catheter will come undone (delamination). For the typically shaped catheter balloon, a balloon with a conical or ellipsoidal body and two necks, the outward pressure exerted on the balloon pushes the balloon material away from the catheter body or shaft. Longer necks with more attachment surface area are needed to securely attach the balloon to the catheter and prevent delamination due to the forces of pressure. This, in turn, creates longer balloons at the catheter distal tip that are more difficult to steer and precisely contact with target tissue.
When ablating around a pulmonary vein ostium, the success of the treatment may depend in part on whether there is adequate contact between the treatment element of the ablation device and the target tissue. Positioning the treatment element at the treatment site can be difficult, as the heart may be beating during the procedure. It may be beneficial to position at least a portion of the ablation device (for example, a portion of the treatment element) within the pulmonary vein in order to anchor the treatment element against the target tissue. However, although ablation of the pulmonary vein ostia may be an effective treatment for arrhythmia, ablation too far within the pulmonary vein, often referred to as being deep within the pulmonary vein, may cause adverse results, such as stenosis.
Another challenge presented by current ablation methods is the warming of the treatment element during cryoablation procedures. For example, a cryoballoon is cooled to a temperature sufficient to ablate tissue by the expansion and circulation of a coolant or cryogenic fluid within the cryoballoon. The effectiveness of the ablation procedure depends in part on the temperature of the ablation element, and it is therefore important that the treatment element, such as a cryoballoon, is maintained at ablation temperatures. However, the circulation of warm blood around the cryoballoon may increase the temperature of the cryoballoon, which may also increase the demand for coolant flow with the cryoballoon at increased flow rates, increased pressure, and/or increased cooling capacity of the system. Such demands may increase the risk of cryoballoon rupture and other system failures.
In light of the above, it is desirable to provide a cryoablation catheter with a shortened distal tip that not only is more easily manipulated within small spaces, but that also includes a balloon that is more resistant to delamination from the catheter body or shaft by making use of the balloon pressure to help reduce the tensile stress on the sealing or bonding agent. Currently used devices with balloons having everted necks experience the opposite effect, with the balloon pressure contributing to delamination. Additionally, glue joints are not particularly good at resisting tensile stress, unless in compression. It is further desirable to provide a method of using a cryoablation catheter with a shortened distal tip. It is a further desirable to provide a system and device that allows for accurate positioning of a treatment element against target tissue without causing ablation deep within the pulmonary vein, and that minimizes the warming effect of blood flow proximate the treatment element.